The present invention relates to a switching network with crosstalk elimination capability for use in a crossbar and/or electronic telephone/data exchange systems.
In telephone/data exchange systems, crosstalk caused by a switching network has a great adverse effect upon performance of the exchange. For this reason, various methods for reducing the crosstalk are proposed. For instance, such crosstalk is caused on speech paths through switching elements such as relays or electronic crosspoints and wiring capacitance elements. The crosstalk further causes a disturbance to other speech paths as intelligible crosstalk or unintelligible noise. The smaller the crosstalk becomes, the smaller is the disturbance. However, in the large-scale switching network, the disturbance becomes greater by the accumulation of the crosstalk, which is mainly due to switch capacitance elements of the switching elements, wiring capacitance elements and the like associated with unused incoming lines which are not connected to subscribers as spare incoming lines for the purpose of maintenance and unused outgoing lines which are disconnected from trunk circuits as spare outgoing lines because of traffic carrying capacity and economic reasons.
However, usually, the proportion of those unused incoming lines and outgoing lines as compared with total numbers of incoming lines and outgoing lines, respectively, of a switching network is small because of efficient use and economical use of the exchange. So, crosstalk caused by these unused incoming and outgoing lines is trifling. Rather, in a state where subscribers, links and trunk circuits are physically connected to the switching network, crosstalk due to switch and wiring capacitance elements associated with idle incoming and outgoing lines has a greatly adverse effect upon the switching network. Especially, such crosstalk occurs when semiconductor elements such as MOSFET's are employed as switching elements.
One typical switching network employing MOSFET's as switching elements is disclosed in an article by Bachle et al. entitled "Fully Electronic Space-Division Telephone Exchanges using Semiconductor Crosspoints and Optical Switching," IEEE Transactions on Communications, Vol. COM-22, No. 9, pp 1286-1291 (particularly FIG. 2 on page 1288) September, 1974.